Quantum Physics
Exceptional points in Gaussian channels: diffusion gauging and drift-governed spectrum
Frank Ernesto Quintela Rodríguez
McDonald and Clerk [Phys.\ Rev.\ Research 5, 033107 (2023)] showed that for linear open
quantum systems the Liouvillian spectrum is independent of the noise strength. We first make this noise-independence principle precise in continuous time for multimode bosonic Gaussian Markov
semigroups: for Hurwitz drift, a time-independent Gaussian similarity fixed by the Lyapunov equation gauges away
diffusion for all times, so
eigenvalues and non-diagonalizability are controlled entirely by the drift, while
diffusion determines steady states and the structure of eigenoperators. We then extend the same separation to discrete time for general stable multimode bosonic Gaussian channels: for any stable Gaussian channel, we construct an explicit Gaussian similarity transformation that gauges away
diffusion at the level of the channel parametrization. We illustrate the method with a single-mode squeezed-reservoir Lindbladian and with a non-Markovian family of single-mode Gaussian channels, where the exceptional-point
manifolds and the associated gauging covariances can be obtained analytically.
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Quantum Physics
Experimental prime factorization via the feedback quantum control
K. B. Hari Krishnan, Vishal Varma and T. S. Mahesh
Prime factorization on
quantum processors is typically implemented either via
circuit-based approaches such as Shor's
algorithm or through
Hamiltonian optimization methods based on adiabatic, annealing, or variational techniques. While Shor's
algorithm demands high-fidelity
quantum gates,
Hamiltonian optimization schemes, with
prime factors encoded as degenerate ground states of a problem
Hamiltonian, generally require substantial classical post-processing to determine control parameters. We propose an all-
quantum, measurement-based feedback approach that iteratively steers a
quantum system toward the target ground state, eliminating the need for classical computation of drive parameters once the problem
Hamiltonian is determined and realized. As a proof of principle, we experimentally factor the biprime 551 using a three-
qubit NMR
quantum register and numerically analyze the robustness of the method against control field-errors. We further demonstrate scalability by numerically implementing the FALQON factorization of larger biprimes, 9,167 and 2,106,287, using 5 and 9
qubits, respectively.
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Quantum Physics
Quantum Metrology under Coarse-Grained Measurement
Byeong-Yoon Go, Geunhee Gwak, Young-Do Yoon et al. (+4 more)
While
quantum metrology enables measurement precision beyond classical limits, its performance is often susceptible to experimental imperfections. Most prior studies have focused on imperfections in
quantum states and operations. Here, we investigate the effect of coarse graining in
quantum measurement through both theoretical analysis and experimental demonstration. Using an interferometer with a squeezed
vacuum and a
laser input, we analyze how coarse graining in homodyne detection affects the precision of phase estimation. We evaluate the Fisher information under various coarse-graining conditions and determine, in each case, an optimal estimation strategy that saturates the Cramér-Rao bound. Remarkably, even extremely coarse-grained measurement – with only two bins – enables phase estimation beyond the standard
quantum limit and even achieves a precision that follows the Heisenberg scaling. We experimentally demonstrate
quantum-enhanced phase estimation under coarse-grained homodyne detection. To determine an optimal estimation strategy, we employ the method of moments and present calibration procedures that enable its application to general experimental settings. Using only two bins, we observe a
quantum enhancement of 1.2 dB compared to the classical method using the ideal measurement, improving towards 3.8 dB as the bin number increases. These results highlight a practical pathway to achieving
quantum enhancement under the presence of severe experimental imperfections.
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All authors Byeong-Yoon Go, Geunhee Gwak, Young-Do Yoon, Sungho Lee, Nicolas Treps, Jiyong Park, Young-Sik Ra
Quantum Physics
Robust Quantum Algorithmic Binary Decision-Making on Gaussian Signals
Aishwarya Majumdar and Yuan Liu
A relevant signal in the
quantum domain may manifest as a displacement or a squeezing operator in the bosonic phase space. For a real parameter $\beta$ embedded in such a Gaussian operator, the task of determining if $\beta \in [\beta_{-th}, \beta_{+th}]$ for real asymmetric thresholds $(\beta_{-th} \ne -\beta_{+th})$ is a binary decision problem. We propose a framework, the generalized
quantum signal processing interferometry (GQSPI), to solve this parameter detection problem by recasting the practical task of active binary hypothesis testing on
quantum systems to a
polynomial approximation problem. We achieve a small decision error probability $p_{\text{err}}$ on the order of $\mathcal{O}(\frac{1}{d}\log{(d)})$, with $d$ as the
circuit depth. We analyze the protocol when (i) $\beta$ is a deterministic parameter, and (ii) when $\beta$ is drawn randomly from a known prior distribution. The GQSPI protocol is also shown to be robust under oscillator dephasing noise. We further extend our protocol from two thresholds to more general multi-threshold cases. Overall, the proposed framework enables decision-making over arbitrary thresholds for any general Gaussian signal in a single or a few shots.
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Quantum Physics · Cross-listed from cond-mat.mes-hall
Helical Current of Propagating Dirac Electrons and Geometric Coupling to Chiral Environments
Ju Gao and Fang Shen
We show that a propagating Dirac electron with intrinsic
spin generically carries a real–space helical conserved current, even in the absence of orbital angular momentum. Using exact Dirac eigenstates in cylindrical confinement, we demonstrate that this helical structure possesses definite handedness, persists into evanescent regions, and is characterized by a
geometric helix pitch independent of the longitudinal de~Broglie wavelength. This intrinsic helical geometry enables a local
geometric coupling between a propagating electron and a
chiral environment, yielding chirality–dependent
spin selectivity through current geometry rather than through a
spin–orbit coupling term.
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Quantum Physics
Echoed Random Quantum Metrology
Dong-Sheng Liu, Zi-Jie Chen, Ziyue Hua et al. (+8 more)
Quantum metrology typically demands the preparation of exotic
quantum probe states, such as entangled or squeezed states, to surpass classical limits. However, the need for carefully calibrated system parameters and finely optimized
quantum controls imposes limitations on scalability and robustness. Here, we circumvent these limitations by introducing an echoed random process that achieves sensitivity approaching the Heisenberg limit while remaining blind to the random probe state. We demonstrate that by simply driving a Kerr nonlinear mode with random pulses, the emergence of sub-Planck phase-space structures grants high sensitivity, eliminating the need for complex
quantum control. The protocol is statistically robust, yielding high performance across broad driving parameter ranges while exhibiting resilience to control fluctuations and
photon loss. Broadly applicable to both bosonic and
qubit platforms, our work reveals a practical, hardware-efficient, scalable, and optimization-free route to
quantum-enhanced metrology in high-dimensional
Hilbert spaces.
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All authors Dong-Sheng Liu, Zi-Jie Chen, Ziyue Hua, Yilong Zhou, Qing-Xuan Jie, Weizhou Cai, Ming Li, Luyan Sun, Chang-Ling Zou, Xi-Feng Ren, Guang-Can Guo
Quantum Physics · Cross-listed from cond-mat.mes-hall
Alexander S. Mayorov, Ping Wang, Xiaokai Yue et al. (+16 more)
Graphene enables precise carrier-density control via gating, making it an ideal platform for studying electronic interactions. However, sample inhomogeneities often limit access to the low-density regimes where these interactions dominate. Enhancing carrier mobility is therefore crucial for exploring fundamental properties and developing device applications. Here, we demonstrate a significant reduction in external inhomogeneity using a double-layer
graphene architecture separated by an ultra-thin hexagonal boron nitride layer. Mutual screening between the layers reduces scattering from random Coulomb potentials, resulting in a
quantum mobility exceeding. Shubnikov de-Haas oscillations emerge at
magnetic fields below 1 mT, while integer
quantum Hall features are observed at 0.002T. Furthermore, we identify a fractional
quantum Hall plateau at a filling factor of at 2T. These results demonstrate the platform's suitability for investigating strongly correlated electronic phases in
graphene-based
heterostructures.
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All authors Alexander S. Mayorov, Ping Wang, Xiaokai Yue, Biao Wu, Jianhong He, Di Zhang, Fuzhuo Lian, Siqi Jiang, Jiabei Huang, Zihao Wang, Qian Guo, Kenji Watanabe, Takashi Taniguchi, Renjun Du, Rui Wang, Baigeng Wang, Lei Wang, Kostya S. Novoselov, Geliang Yu
Quantum Physics
Wigner's Friend as a Circuit: Inter-Branch Communication Witness Benchmarks on Superconducting Quantum Hardware
Christopher Altman
We implement and
benchmark on IBM
Quantum hardware the
circuit family proposed by Violaris for estimating operational inter-branch communication witnesses, defined as correlations in classical measurement records produced by compiled Wigner's-friend-style
circuits. We realize a five-
qubit instance of the protocol as an inter-register message-transfer pattern within a single
circuit, rather than physical signaling, and evaluate its behavior under realistic device noise and compilation constraints. The
circuit encodes branch-conditioned
evolution of an observer subsystem whose dynamics depend on a control
qubit, followed by a controlled transfer operation that probes correlations between conditional measurement contexts. Executing on the ibm_fez backend with 20000 shots, we observe population-based visibility of 0.877, coherence witnesses of 0.840 and -0.811 along orthogonal axes, and a phase-sensitive magnitude of approximately 1.17. While the visibility metric is insensitive to some classes of dephasing, the coherence witnesses provide complementary sensitivity to off-diagonal noise. This work does not test or discriminate among interpretations of
quantum mechanics. Instead, it provides a reproducible operational constraint pipeline for evaluating detectability of non-ideal channels relative to calibrated device noise.
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Quantum Physics
Engineering quantum Mpemba effect by Liouvillian skin effect
Xiang Zhang, Chen Sun and Fuxiang Li
We propose a novel approach to engineer the
quantum Mpemba effect (QME)-wherein an initial state farther from the steaty state relaxes faster than a closer one-by the Liouvillian skin effect (LSE) in open
quantum systems. We show that, in the open
quantum chain with LSE, QME can be easily realized by considering only the spatial profile of initial states, since the initial states localized on the left or right edges experience distinctive relaxation process (algebraic or exponential decay). This approach circumvents the necessity of careful initial-state design and fine-tuning of control parameter. Moreover, when the initial correlation
matrix contains off-diagonal elements, we uncover a new kind of QME which manifest as two crossings in the
Hilbert-Schmidt distance at different times. This work unveils the deep connection between QME and LSE, and provides a physically intuitive understanding of QME and straightforward pathway for the initial state preparation thereby enabling readily accessible experimental preparation.
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Quantum Physics
Matheus V. Scherer, Lea F. Santos and Alexandre D. Ribeiro
We study a general bipartite
quantum system consisting of a
spin interacting with a bosonic field, with the initial state prepared as the product of a
spin coherent state and a canonical coherent state. Our goal is to develop a semiclassical framework to describe the
entanglement dynamics between these two subsystems. Using appropriate approximations, we derive a semiclassical expression for the
entanglement entropy that depends exclusively on the trajectories of the underlying classical description. By analytically extending the classical phase space into the complex domain, we identify additional complex trajectories that significantly improve the accuracy of the semiclassical description. The inclusion of these complex trajectories allows us to capture the
entanglement dynamics with remarkable precision, even well beyond the Ehrenfest time. The approach is illustrated with a representative example, where the role of real and complex trajectories in reproducing the
quantum entanglement entropy is explicitly demonstrated.
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Quantum Physics
Universal Digitized Counterdiabatic Driving
Takuya Hatomura
Counterdiabatic driving realizes parameter displacement of an energy eigenstate of a given parametrized
Hamiltonian using the adiabatic gauge potential. In this paper, we propose a universal method of digitized counterdiabatic driving, constructing the adiabatic gauge potential in a digital way with the idea of universal counterdiabatic driving. This method has three advantages over existing universal counterdiabatic driving and/or digitized counterdiabatic driving: it does not introduce any many-body and/or nonlocal interactions to an original target
Hamiltonian; it can incorporate infinite nested commutators, which constitute the adiabatic gauge potential; and it gives explicit expression of rotation angles for digital implementation. We show the consistency of our method to the exact theory in an analytical way and the effectiveness of our method with the aid of numerical simulations.
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Quantum Physics · Cross-listed from cond-mat.supr-con
Reaching the intrinsic performance limits of superconducting nanowire single-photon detectors up to 0.1 mm wide
Kristen M. Parzuchowski, Eli Mueller, Bakhrom G. Oripov et al. (+13 more)
Superconducting nanowire single-
photon detectors (SNSPDs) combine high detection efficiency, low noise, and excellent timing resolution, making them a leading platform for
photon-counting applications. However, despite decades of materials and fabrication research, detector performance has never been shown to match theoretical performance expectations. Here, we demonstrate for the first time in situ tuning of a detector from its typical, suboptimal operation, to a regime limited only by material quality, allowing the device to reach its intrinsic performance limit. Our approach is based on current-biased superconducting "rails" placed on either side of the detector that redistribute current across its width to achieve its peak performance. This technique reduces the dark count rate by ten orders of magnitude. Further, we show operation at this intrinsic performance limit for devices up to 0.1 mm wide, and also demonstrate near-unity internal detection efficiency (IDE) at a wavelength of 4um for a 20um-wide detector–a factor of 20 wider than the current state of the art. This work enables future detectors to overcome the Pearl limit for device width, paving the way for arbitrarily large detectors.
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All authors Kristen M. Parzuchowski, Eli Mueller, Bakhrom G. Oripov, Benedikt Hampel, Ravin A. Chowdhury, Sahil R. Patel, Daniel Kuznesof, Emma K. Batson, Ryan Morgenstern, Robert H. Hadfield, Varun B. Verma, Matthew D. Shaw, Jason P. Allmaras, Martin J. Stevens, Alex Gurevich, Adam N. McCaughan
Quantum Physics
Bandwidth-Cost Reduction for Photon-Matter Simulation at the Single-Photon Level
Romain Piron and Akihito Soeda
Simulations of
quantum dynamics of traveling
photons interacting with matter can be used to model and design photonic
quantum-network components. Such simulations require selecting a finite set of photonic modes, where smaller sets are more desirable for computational efficiency. In this work, however, we show that opting for smaller subsets alters simulation results, if done naively. We therefore provide a consistency condition that can be used to calibrate the simulation input parameters to increase efficiency while preserving accuracy, simultaneously. This condition is then used to derive a simple prescription that reduces the propagation cost by two order of magnitude in a waveguide
benchmark. Finally, we extend the same calibration principle to a two-dimensional atomic array, demonstrating the simultaneous benefits beyond analytically solvable waveguide models.
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Quantum Physics
Frictional work and entropy production in integrable and non-integrable spin chains
Vishnu Muraleedharan Sajitha, Matthew J. Davis and L. A. Williamson
The maximum work extractable from a
quantum system is achieved when the system is driven adiabatically. Frictional work $\langle W\rangle_\mathrm{fric}$ then quantifies the difference in work output between adiabatic and non-adiabatic driving. Here we show that frictional work in a non-integrable
spin chain is well-characterized by the diagonal
entropy production $\Delta S_\mathrm{d}$ associated with the build up of
quantum coherence. We show that, over a broad range of parameters, $\langle W\rangle_\mathrm{fric}\approx T_\tau\Delta S_\mathrm{d}$, with $T_\tau$ the effective temperature of the final time-evolved state. The relationship breaks down for fast protocols at low temperatures, in which case frictional work is instead well-described by the
quantum relative
entropy between the time-evolved state and a Gibbs-state approximation of the adiabatic state. We compare our results to those obtained from an integrable
spin chain, in which case the system is no longer described by a single temperature. In this case, the frictional work is described by a sum of terms for each independent subspace of the
spin chain, which are at different effective temperatures. Finally, we show how integrability breaking can enhance work extraction in the adiabatic limit, but degrade work extraction in sufficiently non-adiabatic regimes.
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Quantum Physics
Automated quantum circuit optimization with randomized replacements
Marcin Szyniszewski, Aleks Kissinger, Noah Linden et al. (+1 more)
Quantum circuit optimization - the process of transforming a
quantum circuit into an equivalent one with reduced time and space requirements - is crucial for maximizing the utility of current and near-future
quantum devices. While most automated optimization techniques focus on transforming
circuits into equivalent ones that implement the same
unitary, we show that substantial new opportunities for resource reduction can be achieved by (1) allowing approximate local transformations and (2) employing mixed
quantum channels to approximate pure
circuits. Our novel automated protocol for approximate
circuit rewriting is a refined
evolution of automated optimization techniques based on the ZX-calculus, where we add a greedy strategy that selectively replaces ZX-diagrams with small phase angles with
stochastic mixtures of the identity and carefully chosen over-rotations, which are designed to reduce the overall gate count in expectation while staying within a strict error budget. This approach yields modest two-
qubit gate count reduction in random
quantum circuits, and achieves a substantial reduction in structured
circuits such as the
quantum Fourier transform. Fundamentally, our protocol converts experimental noise due to gate applications into deliberately engineered random noise, outperforming many other approximation methods on average. These results highlight the potential of mixed-channel approximations to enhance future
quantum circuit performance, suggesting new directions for resource-aware automated
quantum compilation beyond pure
unitary channels.
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All authors Marcin Szyniszewski, Aleks Kissinger, Noah Linden, Paul Skrzypczyk
Quantum Physics
Improved cryptographic security in teleportation with q-deformed non-maximal entangled states
Prabal Dasgupta and Debashis Gangopadhyay
In this work the machinery of q-deformed
algebras are used to enhance cryptographic security during teleportation. We use q-deformed harmonic oscillator states to develop a novel method of teleportation. The deformed states can be expressed in terms of standard oscillator states and the expressions contain certain arbitrary functions of $q$. It is the presence of these arbitrary functions that allows an enhancement of cryptographic security. The specifics are : (a) q-deformed Bell-like states are constructed which reduce to the usual Bell states when the deformation parameter $q\rightarrow 1$. These deformed states form an orthonormal basis for q-deformed entangled bipartite states when certain arbitrary functions of $q$ satisfy a constraint. (b) We discuss the generalisation of the usual teleportation protocol with non-maximally entangled states. This generalisation is then employed to construct two new protocols using q-deformed non-maximally entangled states. These states have additional parameters and these have to be shared for decryption after teleportation. Consequently, the cryptographic security is improved.
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Quantum Physics
Chaitanya Gupta and Anthony J. Short
We consider discrete spacetime models known as
quantum walks, which can be used to simulate Dirac particles. In particular we look at
fermion doubling in these models, in which high momentum states yield additional low energy solutions which behave like Dirac particles. The presence of doublers carries over to the `second quantised' version of the walks represented by
quantum cellular automata, which may lead to spurious solutions when introducing interactions. Moreover, we also consider pseudo-doublers, which have high energy but behave like low energy Dirac particles, and cause potential problems regarding the stability of the
vacuum. To address these issues, we propose a family of
quantum walks, that are free of these doublers and pseudo-doublers, but still simulate the Dirac equation in the continuum limit. However, there remain a small number of additional low energy solutions which do not directly correspond to Dirac particles. While the conventional Dirac walk always has a zero probability for the walker staying at the same point after a single time step, we obtain the family of walks by allowing this probability to be non-zero.
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Quantum Physics · Cross-listed from hep-lat
Magic of discrete lattice gauge theories
Gianluca Esposito, Simone Cepollaro, Luigi Cappiello et al. (+1 more)
Simulation of
quantum field theories and fundamental interactions are one of the most challenging tasks in modern particle physics. Classical computers generally fail to reproduce accurate results when it comes to strongly coupled theories such as QCD. Recent developments in
quantum technologies open up the possibility of simulating such physical regimes by using
quantum computers. In this paper, we study the
quantum resource related to the simulability of a
quantum theory, i.e. non-stabilizerness for
Lattice Gauge Theory (LGT) with discrete
symmetry gauge groups. We show that enforcing gauge constraints for $\mathbb{Z}_l$ LGTs has no cost in terms of this resource and discuss the relation between non-abelianity of the gauge group with the average non-stabilizerness of the gauge invariant
Hilbert space.
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All authors Gianluca Esposito, Simone Cepollaro, Luigi Cappiello, Alioscia Hamma
Quantum Physics · Cross-listed from math.CT
Quantum Coherence Spaces Revisited: A von Neumann (Co)Algebraic Approach
Thea Li and Vladimir Zamdzhiev
We describe a categorical model of MALL (Multiplicative Additive Linear Logic) inspired by the Heisenberg-Schrödinger duality of finite-dimensional
quantum theory. Proofs of formulas with positive logical polarity correspond to CPTP (completely positive trace-preserving) maps in our model, i.e. the
quantum operations in the Schrödinger picture, whereas proofs of formulas with negative logical polarity correspond to CPU (completely positive unital) maps, i.e. the
quantum operations in the Heisenberg picture. The mathematical development is based on noncommutative geometry and finite-dimensional von Neumann (co)
algebras, which can be defined as special kinds of (co)monoid objects internal to the category of finite-dimensional operator spaces.
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Quantum Physics
Jue Xu, Chu Zhao, Xiangran Zhang et al. (+2 more)
Entanglement is not only the origin of exotic
quantum phenomena, but also widely regarded as the fundamental barrier to classical simulation of
quantum dynamics. We overturn this intuition: for predicting local observables under
Hamiltonian evolution,
entanglement in the
quantum state actually heals the classical simulation error in the Heisenberg picture. Classical
algorithms that propagate observables in the Pauli basis with proper truncation have shown remarkable empirical success in simulating noiseless
quantum dynamics, yet all prior rigorous guarantees required noise or randomness—leaving the physically relevant noiseless regime without theoretical foundation. To close this gap, we prove that the truncation error of Low-weight Pauli Dynamics (LPD) admits an average-case bound without assuming randomness, provided the state is sufficiently entangled. Since tensor-network methods efficiently simulate low-
entanglement states while LPD thrives precisely in the complementary regime, together they extend rigorous classical simulation to longer times, sharpening the boundary between classically simulable and genuinely
quantum dynamics.
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All authors Jue Xu, Chu Zhao, Xiangran Zhang, Shuchen Zhu, Qi Zhao
Quantum Physics
Improving the efficiency of QAOA using efficient parameter transfer initialization and targeted-single-layer regularized optimization with minimal performance degradation
Shubham Patel and Utkarsh Mishra
Quantum approximate optimization
algorithm (QAOA) have promising applications in combinatorial optimization problems (COPs). We investigated the MaxCut problem in three different families of graphs using QAOA ansats with parameter transfer initialization followed by targeted single layer optimization. For 3 regular (3R), Erdos Renyi (ER), and Barabasi Albert (BA) graphs, the parameter transfer approach achieved mean approximation ratios of 0.9443 for targeted-single layer optimization as compared to 0.9551 of full optimization. It represents 98.88 percent optimal performance, with 8.06 times computational speedup in unweighted graphs. But, in weighted graph families, optimal performance is relatively low (less than 90 percent) for higher nodes graph, suggesting parameter transfer followed by targeted-single-layer optimization is not ideal for weighted graph families, however, we find that for some weighted families (weighted 3-regular) this approach works perfectly. In 8.92 percent test cases, targeted single layer optimization outperformed the full optimization, indicating that complex parameter landscape can trap full optimization in sub-optimal local minima. To mitigate this inconsistency, ridge (L2) regularization is used to smoothen the solution landscape, which helps the optimizer to find better optimum parameters during full optimization and reduces these inconsistent test cases from 8.92 percent to 3.81 percent. This work demonstrates that efficient parameter initialization and targeted-single-layer optimization can improve the efficiency of QAOA with minimal performance degradation.
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Quantum Physics
Singular band Induced by Long-Range Interaction Enables Unsplit Spreading of Localized Excitations
Jian-Feng Wu, Yi Huang and Yu-Xiang Zhang
In conventional
lattice models, the dispersion relation $\omega(k)$ is assumed to be a smooth function which is periodic over the first Brillouin Zone. However, in subwavelength atom arrays the dispersion of the light-mediated long-range interaction is singular at the light cone. This observation
prompts us to ask what effect arises from such band singularity. Here we demonstrate that, due to the
topology of smooth functions defined over the periodic Brillouin zone, smoothness implies the splitting of an initially localized excitation into counter-propagating wave packets. Consequently, unsplit spreading can occur only when $\omega(k)$ develops singular features, precisely what long-range interactions enable. We identify unsplit spreading in 1D toy tight-bounding models and the realistic models of 1D and 2D subwavelength atomic arrays. Our work establishes unsplit spreading as an experimentally accessible, smoking-gun signature of singular band structure.
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Quantum Physics
Fractional squeezing: spectra and dynamics from generalized squeezing Hamiltonian with fractional orders
Sahel Ashhab
We generalize the generalized-squeezing problem to include fractional values of the squeezing order $n$. This approach allows us to determine the locations of critical points at which qualitative changes in behaviour occur and accurately predict the behaviour at these critical points, which are challenging for conventional computational methods. Based on our numerical calculations, we identify with a high degree of confidence the point at which the spectrum turns from continuous to discrete and the point at which oscillations turn from having asymptotically infinite amplitudes to having finite amplitudes. Furthermore, we numerically investigate the behaviour in the large $n$ regime and provide an intuitive explanation for the numerical results.
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Quantum Physics
Quantum-HPC hybrid computation of biomolecular excited-state energies
Kentaro Yamamoto, Riku Masui, Takahito Nakajima et al. (+16 more)
We develop a workflow within the ONIOM framework and demonstrate it on the hybrid computing system consisting of the supercomputer Fugaku and the Quantinuum Reimei trapped-ion
quantum computer. This hybrid platform extends the layered approach for biomolecular chemical reactions to accurately treat the active site, such as a
protein, and the large and often weakly correlated molecular environment. Our result marks a significant milestone in enabling scalable and accurate simulation of complex biomolecular reactions
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All authors Kentaro Yamamoto, Riku Masui, Takahito Nakajima, Miwako Tsuji, Mitsuhisa Sato, Peter Schow, Lukas Heidemann, Matthew Burke, Philipp Seitz, Oliver J. Backhouse, Juan W. Pedersen, John Children, Craig Holliman, Nathan Lysne, Daichi Okuno, Seyon Sivarajah, David Muñoz Ramo, Alex Chernoguzov, Ross Duncan
Quantum Physics
Enhancing the Size of Phase-Space States Containing Sub-Planck-Scale Structures via Non-Gaussian Operations
Arman and Prasanta K. Panigrahi
We observe a metrological advantage in phase-space sensitivity for
photon-added cat and kitten states over their original forms, due to phase-space broadening from increased amplitude via
photon addition, albeit with higher energy cost. Using accessible non-classical resources, weak squeezing and displacement, we construct a squeezed state and two superposed states: the squeezed cat state and the symmetrically squeezed state. Their
photon-added variants are compared with parity-matched cat and KSs using
quantum Fisher information and fidelity. The QFI isocontours reveal regimes where KS exhibit high fidelity and large amplitude, enabling their preparation via Gaussian operations and
photon addition. Similar regimes are identified for cat states enhanced by squeezing and
photon addition, demonstrating improved metrological performance. Moreover, increased amplitude and thus larger phase-space area reduces the size of interferometric fringes, enhancing the effectiveness of
quantum error correction in cat codes.
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Quantum Physics
Machine Failure Detection Based on Projected Quantum Models
Larry Bowden, Qi Chu, Bernard Cena et al. (+4 more)
Detecting machine failures promptly is of utmost importance in industry for maintaining efficiency and minimizing downtime. This paper introduces a failure detection
algorithm based on
quantum computing and a statistical change-point detection approach. Our method leverages the potential of projected
quantum feature maps to enhance the precision of anomaly detection in machine monitoring systems. We empirically validate our approach on
benchmark multi-dimensional time series
datasets as well as on a real-world
dataset comprising IoT sensor readings from operational machines, ensuring the practical relevance of our study. The
algorithm was executed on IBM's 133-
qubit Heron
quantum processor, demonstrating the feasibility of integrating
quantum computing into industrial maintenance procedures. The presented results underscore the effectiveness of our
quantum-based failure detection system, showcasing its capability to accurately identify anomalies in noisy time series data. This work not only highlights the potential of
quantum computing in industrial diagnostics but also paves the way for more sophisticated
quantum algorithms in the realm of predictive maintenance.
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All authors Larry Bowden, Qi Chu, Bernard Cena, Kentaro Ohno, Bob Parney, Deepak Sharma, Mitsuharu Takeori
Quantum Physics
Tensor-based phase difference estimation on time series analysis
Shu Kanno, Kenji Sugisaki, Rei Sakuma et al. (+3 more)
We propose a phase-difference estimation
algorithm based on the tensor-network
circuit compression, leveraging time-
evolution data to pursue scalability and higher accuracy on a
quantum phase estimation (QPE)-type
algorithm. Using tensor networks, we construct
circuits composed solely of nearest-neighbor gates and extract time-
evolution data by four-type
circuit measurements. In addition, to enhance the accuracy of time-
evolution and state-preparation
circuits, we propose techniques based on algorithmic error mitigation and on iterative
circuit optimization combined with merging into
matrix product states, respectively. Verifications using a noiseless simulator for the 8-
qubit one-dimensional Hubbard model using an ancilla
qubit show that the proposed
algorithm achieves accuracies with 0.4–4.7% error from a true energy gap on an appropriate time-step size, and that accuracy improvements due to the algorithmic error mitigation are observed. We also confirm the enhancement of the overlap with
matrix product states through iterative optimization. Finally, the proposed
algorithm is demonstrated on IBM Heron devices with Q-CTRL error suppression for 8-, 36-, and 52-
qubit models using more than 4,000 2-
qubit gates. These largest-scale demonstrations for the QPE-type
algorithm represent significant progress not only toward practical applications of near-term
quantum computing but also toward preparation for the era of error-corrected
quantum devices.
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All authors Shu Kanno, Kenji Sugisaki, Rei Sakuma, Jumpei Kato, Hajime Nakamura, Naoki Yamamoto
Quantum Physics
Optimized Slice-Phase Control of Mirror Pulse in Cold-Atom Interferometry with Finite Response Time
Xueting Fang, Doudou Wang, Kun Yuan et al. (+6 more)
Atom interferometers require both high efficiency and robust performance in their mirror pulses under experimental inhomogeneities. In this work, we demonstrated that
quantum optimal control designed mirror pulse significantly enhance interferometer performance by using novel adaptive sliced structure. Using gradient ascent pulse engineering (GRAPE), optimized mirror pulse for a Mach-Zehnder light-pulse atom interferometer was designed by discretizing the control into non-uniform phase slices. This design broadened the tolerence to experimentally relevant variations in detuning $[-\Omega_0,\Omega_0]$ and Rabi frequency $[0.1\times\Omega_0,1.9\times\Omega_0]$ ($\Omega_0=2\pi\times25$ kHz), while maintaining high transfer efficiency even when the response-time delays up to 1.6 $\rm{\mu s}$. The optimized pulse was found to be robust to coupling inhomogeneity and velocity spread, offering a significant improvement in robustness over conventional pulse. The adaptive pulse slicing method provides a minimalist strategy that reduces experimental complexity while enhancing robustness and scalability, offering an innovative scheme for
quantum optimal control in high precision atom interferometry.
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All authors Xueting Fang, Doudou Wang, Kun Yuan, Jie Deng, Qin Luo, Xiaochun Duan, Minkang Zhou, Lushuai Cao, Zhongkun Hu
Quantum Physics
Bright Pulsed Squeezed Light for Quantum-Enhanced Precision Microscopy
Alex Terrasson, Lars Madsen, Joel Grim et al. (+1 more)
Squeezed states of light enable enhanced measurement precision by reducing noise below the standard
quantum limit. A key application of squeezed light is nonlinear microscopy, where state-of-the-art performance is limited by photodamage and
quantum-limited noise. Such microscopes require bright, pulsed light for optimal operation, yet generating and detecting bright pulsed squeezing at high levels remains challenging. In this work, we present an efficient technique to generate high levels of bright picosecond pulsed squeezed light using a $\chi^2$ optical parametric amplification process in a waveguide. We measure $-3.2~\mathrm{dB}$ of bright squeezing with optical power compatible with nonlinear microscopy, as well as $-3.6~\mathrm{dB}$ of
vacuum squeezing. Corrected for losses, these squeezing levels correspond to $-15.4^{+2.7}_{-8.7}~\mathrm{dB}$ of squeezing generated in the waveguide. The measured level of bright amplitude pulsed squeezing is to our knowledge the highest reported to date, and will contribute to the broader adoption of
quantum-enhanced nonlinear microscopy in biological studies.
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All authors Alex Terrasson, Lars Madsen, Joel Grim, Warwick Bowen
Quantum Physics
Spectator-transition crosstalk in a spin-3/2 silicon-vacancy qudit in silicon carbide revealed by broadband Ramsey interferometry
Jun-Jae Choi, Seung-Jae Hwang, Seoyoung Paik et al. (+9 more)
Color-center
spins in 4H-SiC offer a rare combination of wafer-scale materials maturity with long
spin coherence and chip-level photonics, making them promising building blocks for scalable
quantum technologies. In particular, the silicon vacancy hosts an S=3/2 ground state, a native qudit that enables compact encodings and subspace-selective control but also introduces spectator transitions: short, detuned pulses can coherently drive nonaddressed level pairs and create crosstalk. Here we use broadband Ramsey interferometry to reveal and quantify such spectator-transition crosstalk. Experimentally, the Ramsey
Fourier spectra display multiple lines beyond the addressed single-
quantum transition. Analytically, we map each line to a pairwise energy difference between qudit levels of the rotating-frame
Hamiltonian and assign its weight via compact amplitudes set by the prepared state and the microwave pulse parameters, predicting a deterministic six-branch structure. Numerical time-domain propagation with the experimental sampling reproduces the detuning map, and the measured peak positions coincide with the analytic branch lines without frequency fitting. Together these results provide a practical, spectator-aware framework for multilevel control in the silicon-vacancy qudit. The approach offers clear guidance to suppress crosstalk or, conversely, to exploit spectator lines, e.g., as additional constraints for in situ pulse calibration and for phase-sensitive
quantum state and process estimation.
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All authors Jun-Jae Choi, Seung-Jae Hwang, Seoyoung Paik, Juhwan Kim, Jawad Ul-Hassan, Nguyen Tien Son, Hiroshi Abe, Takeshi Ohshima, Jaekwon Suk, Hyeon-Ho Jeong, Dong-Hee Kim, Sang-Yun Lee